Process and apparatus for countercurrent treatment



Oct. 17, 1939. w ED. JR 2,176,429

I PROCESS AND APPARATUS FOR COUNTERCURRENT TREATMENT Filed May 25, 1938A RAFFINATE SOLVENT H EXTRACTlON TOWER 16 HEAT I INTERCHANGER EXTRACTWYNKOOP KIERSTED. JR.

INVENTOR AMZ/ QM ATTORNEY Patented Oct. 11, 1939 PATENT OFFICE PROCESSAND APPARATUS FOR COUNTER CURRENT TREATMENT Wynkoop Kiersted, In,Scandale, N. Y., asaignor to The Texas Company, New York, N. Y., acornotation of Delaware Application May as, 1938, serial No. 209,911

Claims. (01. last-1a) This invention relates to apparatus for a methodof treating one liquid countercurrently with another. It has particularreference to the countercurrcnt treatment of hydrocarbon oils with a 5liquid, such as a selective solvent.

The invention broadly contemplates electing countercurrent treatment ofliquids in a packed tower, wherein at successive points in the tower theliquid phases are separated, subjected to mixing, and returned to thetower at or near-the point of separation, as will be more fullydescribed.

In the treatment of hydrocarbon oil, such as minerallubricating oil, forexample, with a selective solvent, such as furfural, the oil isintroduced to the lower portion of a packed tower,

while the solvent is introduced to the upper portion thereof. Oil andsolvent move countercurrently through the tower, and in doing so formwithin the tower extract andrafllnate phases.

The extract phase is rich in aromatic and naphthenic type constituentsof the oil and accumulates in the bottom of the tower, from which it iscontinuously withdrawn.

The raiiinate phase, on the other hand, comprises the more parafllnicand insoluble constituents of the oil mixed with a small proportion ofthe solvent. This rafllnate phase accumulates in the upper portion ofthe tower and is continuously withdrawn therefrom.

The present invention involves providing, at intervals within the tower,preferably between succeeding sections of packing material, means forseparating extract and ramnate phase liquid, 0 subjecting it to intimatemixing, and returning it to the extraction tower after heating orcooling, if necessary.

By these means, close control of the contact between oil and solvent isefiected. The overall effect is to produce within the extraction towerin a stage counterflow operation, as carried out in a series of separatemixing and settling vessels.

The purpose of the invention, therefore, is to combine in acountercurrent extraction system the simplicity of operation permittedin a conventional packed tower and the extractive efficiency of a stageoperation.

Reference will now be had to the accompanying drawing in order tofurther describe the invention.

In the drawing, the numeral HI designates a vertical cylindrical vesselto which a solvent, such as furfural, is introduced through an inlet ilin the upper portion of the tower, while the oil to be treated isintroduced through an inlet l2-near the bottom. Sprays, or otherdistributing means, it and it are positioned within the go tower throughwhich the solvent and oil, respecconditions somewhat similar to thoseprevailing tively, are distributed'through the packing material.

The packing advantageously consists of screens is, spaced at intervalsthroughout the length of the tower. As indicated, the spacing betweeneach set of three or more screens maybe in; creased so that it isgreater than the distance between the individual screens in eachsection.

It is contemplated, however, that instead of screens the packing maytake some other form. 10 For example, it may consist of nests of Raschigrings, or other material commonly used as packing material, and whichexposes a large surface area of contact. If desired, a combination ofscreens and Raschig rings may be employed. In 15 such case, each sectionof packing may consist of three screens, spaced a short distance apart,with the intervening spaces filled with Raschig rings.

Within the enlarged spaces between each sec- 20 tion of packing anannular channel or trough i6 extends around the interior wall of thevessel l0, and which is adapted to catch and retain liquid flowing intoit from a conical bafiie II. This trough advantageously has an insidearea equal 25 to about of the cross-sectional area of the tower.

The bailie i1 is provided with an orifice at its vertex and its outerperipheral edge extends substantially aboveand partially over the inneredge 80 of the channel IS.

A disk batlie I8 is horizontally disposed a short distance above theorifice in the conical baiile l1.

A bell mouth or funnel type suction element i9 is located below theconical baflle I! and posi- 35 tioned so as to provide a drawoif forliquid accumulating within the vertex of the conical baiiie IT.

A valved pipe 20 is provided for withdrawing from the tower liquidaccumulating in the trough 0 l6. Similarly, a valved pipe 2| is providedfor drawing ofi liquid collecting in the funnel I9. These pipes lead tothe suction side of a pump 22, which acts as a mixer for the liquidsdrawn into this suction, and which discharges the mixed 5 liquidsthrough a heat interchanger 23 to the interior of the tower at a pointjust above the disk baille II.

The phase liquid collecting in the trough i 6 comprises mainly extractphase-or heavy gravity 5o material rich in solvent, while that flowinginto the funnel i8 comprises raflinate phase or lighter gravity materialrich in oil. Thus, the arrangement of bailling is such that these phasesmay be collected separately at successive points in the tower and drawnofi for intimate mixing. The battle it prevents short-circuiting of themixed phases upon their return to the tower.

These liquid phases may be drawn 011 through the pipes 20 and 2! in anydesired proportion.

This permits realizing greater extractive em-.

cienc 1Tb: heat interchanger 23 is employed to either increase thetemperature or reduce the temperature of the mixture being returned tothe tower. For example, where it is desired to maintain a temperaturegradient from top to bottom within the tower, the interchangersat theupper portions of the tower may be used to heat the mixture passingtherethrough, while the interchangers at lower points may be used tocool the returning liquid.

The tower is advantageously provided with settling spaces in the upperand lowermost portions. The ultimate extract phase, comprising solventcontaining dissolved constituents of the oil, is withdrawn from thebottom of the towerthrough -a pipe 24, while the ultimate rafllnatephase is drawn oif from the top of the tower through a pipe 25.

In operation, the oil to be treated may be introduced at or at somewhatabove normal temperature, while the solvent is introduced to the upperportion of the tower at a substantially elevated temperature. Thus, whenemploying 'furfural as the solvent the temperature at the tions.

Obviously, many modifications and variations of the invention, ashereinbefore set forth, may be made without departing from the spiritand scope thereof, and therefore only such limitations should be imposedas are indicated in the appended claims.

- I claim:

1. In the countercurrent treatment of hydrocarbon oil with'a solvent toextract from the oil undesired constituents, the method comprisingpassing the oil'through a vertical tower provided with a plurality ofsections of packing spaced vertically apart, one above the other, andcontaining collecting means between succeeding sections for separatelycollecting extract and raffinate phase liquids, moving a solvent throughsaid tower countercurrently to the oil, withdrawing extract andraiiinate phase liquids accumulating in the spaced portions betweensucceeding sections of packing, mixing said liquids in proportions suchthat the ratio of extraction solvent to oil is substantially greaterthan that existing raflinate phase liquids, moving a solvent throughsaid tower countercurrently to the oil, separately withdrawing extractand ramnate phase liquids accumulating in the spaced portions betweensucceeding sections of packing, re-mixing said liquids in proportionsuch that the ratio of extraction solvent to oil is substantiallygreater than that existing between the fresh solvent and oil enteringthe terminals of the tower, and returning the thus mixed liquid to thesame spaced portion of the tower from which withdrawn.

3. 'In the countercurrenttreatment of hydrocarbon oil with a solvent toseparate the oil into extract and rafiinate phases, the method com- Yprising passing the oil through a packed vertical tower, at verticalintervals throughout the tower segregating the oil and solvent intoextract and raifinate phases, each corresponding extract and raffinatephase being formed at substantially the same elevation within the tower,separately withdrawing the segregated phases, re-mixing thecorresponding extract and raiflnate phases in proportion such that theratioof extraction solvent to oil is substantially different from thatexisting between the fresh solvent and oil entering the terminals of.the tower and returning each resulting mixture to substantially the samepoint within the tower from which withdrawn.

4. In a packed tower for eifecting countercurrent contact betweenmineral oil and a selective solvent the combination comprising aplurality of enlarged settling spaces at vertical intervals throughoutthe' tower between sections of packing material, means for separatingwithin each settling space and at substantially the same level withinthe tower a light gravity phase and a heavy gravity phase, means forseparately withdrawing in predetermined proportions said light and heavyphases separated at each level,

'means for intimately re-mixing the phases withdrawn from each level,and means for returning the resulting mixture to the same settling spacefrom which withdrawn.

5. In a vertical tower for the countercurrent treatment of oil with asolvent the combination comprising a vertical vessel packed with contactpacking material and arranged for countercurrent flow of oil and solventtherethrough, a plurality of enlarged settling spaces at. intervalsthroughout the vessel between sections of packing material, means forseparating within and separately withdrawing from each settling space alight gravity liquid and a heavy gravity liquid, said means comprisingan annular trough extending horizontally around the interior wall ofsaid vessel, a conical baflle surmounting each trough having its outerperipheral edge extending substantially above and beyond the inner edgeof the trough, an orifice in the vertex of I said conical baille, animperforate disk baiiie horizontally disposed above the orifice andspaced a short distance apart therefrom, a receptacle positioned beneaththe conical battle a short distance below the orifice adapted to receiveliquid accumulating in the immediate region of the orifice, a conduitcommunicating between said receptacle and the exterior of the vessel, aseparate conduit communicating between the trough and the exterior ofthe vessel, means exterior of the vessel in communication with both saidconduits for mixing the liquids passing through said conduits, and meansfor returning the mixed liquids back to the interior of the vessel at apoint just above the disk baflie.

- WYNKOOP KIERSTED, JR.

